1. Field of the Invention
The present invention relates to rigid, microcellular organic foams made from naturally occurring organic material. The foam is formed from an organic gel in which the solvent in the gel pores is exchanged with at least one other solvent to produce microscopic pores. The gel is rapidly frozen and then dried to form a microcellular biofoam.
2. Description of Related Art
A myriad of applications exist for strong, low-density, inexpensive materials to manufacture lightweight articles. Synthetic polymers and foams, such as polystyrene, polyurethane, and Styrofoam.RTM., are commonly-used materials for these purposes. A soluble, lightweight material made from corn and wheat is also currently available. A continual demand exists for the development of ever lighter, stronger, cost-effective materials that are biodegradable and made from renewable resources.
The scientific research communities in government and academia have a need for ultralightweight microcellular foams exhibiting a variety of characteristics. Researchers working with materials such as TPX (synthetic methylpentene polymer) and polystyrene have been unable to reach very low densities and create the cell structures desired. The present invention addresses these diverse needs and is a biofoam produced from organic materials derived from biological organisms, such as algae.
Biofoam is distinguishable from another class of ultra-low density materials, namely aerogels, which were developed by another group at Lawrence Livermore National Laboratory. Aerogel is a true gel in which the gel structure must be maintained throughout the production process. In contrast, while the biofoam production process involves a gel stage, the end product is not a gel, but an open-cell rigid foam material similar to polystyrene. The different microscopic structures of the two materials leads to variances in their physical and chemical properties.
For example, the most common aerogel is a silica-based material that will not burn easily. Biofoam is an organic-based material that will burn without producing toxic fumes. The average cell or pore size of aerogel is about 10 times smaller than the pores in the present version of biofoam; aerogel pore diameters are about 0.02-0.03 microns, whereas biofoam cells have diameters of about 0.2-0.3 microns. The smaller pore size of aerogels makes them visibly transparent and better thermal and acoustic insulators than biofoam, although the present form of biofoam is almost transparent and has excellent insulating properties due to its small pore size.
The major advantage of biofoam over aerogel is its lower production cost. Aerogel's complex production process involving supercritical extraction of solvents is time-consuming and expensive when compared to the freeze-drying procedure used in biofoam production. Furthermore, biofoam is a more robust material than aerogel that can withstand greater forces without fracturing or deforming and can be readily machined into different shapes.
A biofoam with an average pore size less than that of the earlier version of biofoam (described in U.S. patent application Ser. No. 08/043,300) would have better insulating properties, making it more competitive with aerogel. The ultrasmall pore size would also result in translucent varieties of biofoam which are useful for certain applications. Therefore, the need exists for an improved version of biofoam having significantly smaller pores.